174

CHEMISTRY (Theory)

Time allowed : 3 hours Maximum Marks : 70

General Instructions:

(i) All questions are compulsory.

(ii) Marks for each question are indicated against it.

(iii) Question numbers 1 to 8 are very short-answer questions and carry 1 mark

each.

(iv) Question numbers 9 to 18 are short-answer questions and carry 2 marks

each.

(v) Question numbers 19 to 27 are also short-answer questions and carry 3 marks

each.

(vi) Question numbers 28 to 30 are long-answer questions and carry 5 marks each.

(vii) Use Log Tables, if necessary, Use of calculators is not allowed.

QUESTION PAPER CODE 56/1/1

1. Write a feature which will distinguish a metallic solid from an ionic solid. 1

2. Define ‘order of a reaction’. 1

3. What is an emulsion? 1

4. Why does NO2 dimerise ? 1

5. Give an example of linkage isomerism. 1

6. A solution of KOH hydrolyses CH3CHClCH

2CH

3 and CH

3CH

2CH

2CH

2Cl.

Which one of these is more easily hydrolysed? 1

7. Draw the structural formula of I-phenylpropan-l-one molecule. 1

8. Give the IUPAC name of H2N – CH

2 – CH

2 - CH = CH

2. 1

175

9. Non-ideal solutions exhibit either positive or negative deviations from Raoult’s law.

What are these deviations and why are they caused? Explain with one example for

each type. 2

10. A reaction is of first order in reactant A and of second order in reactant B. How is

the rate of this reaction affected when (i) the concentration of B alone is increased to

three times (ii) the concentrations of A as well as B are doubled? 2

11. The rate constant for a reaction of zero order in A is 0.0030 mol L –1 s–1. How long

will it take for the initial concentration of A to fall from 0.10 M to 0.075 M ? 2

12. Draw the structures of white phosphorus and red phosphorus. Which one of these

two types of phosphorus is more reactive and why? 2

13. Explain the following observations:

(i) Generally there is an increase in density of elements from titanium (Z = 22) to

copper (Z = 29) in the first series of transition elements.

(ii) Transition elements and their compounds are generally found to be good

catalysts in chemical reactions. 2

14. Name the following coordination compounds according to IUPAC system of nom-

enclature:

(i) [Co(NH3)

4 (H

2O)Cl]Cl

2

(ii) [CrCl2(en)

2]Cl, (en = ethane – 1, 2 – diamine) 2

15. Illustrate the following reactions giving a chemical equation for each:

(i) Kolbe’s reaction,

(ii) Williamson synthesis. 2

16. How are the following conversions carried out?

(i) Benzyl chloride to benzyl alcohol,

(ii) Methyl magnesium bromide to 2-methylpropan-2-ol. 2

176

17. Explain the following terms. :

(i) Invert sugar

(ii) Polypeptides

OR

Name the products of hydrolysis of sucrose. Why is sucrose not a reducing sugar? 2

18. What are essential and non-essential amino acids in human food? Give one example

of each type. 2

19. The well known mineral fluorite is chemically calcium fluoride. It is known that in

one unit cell of this mineral there are 4 Ca2+ ions and 8 F– ions and that Ca2+ ions are

arranged in a fcc lattice. The F– ions fill all the tetrahedral holes in the face centred

cubic lattice of Ca2+ ions. The edge of the unit cell is 5.46x10–8

cm in length. The

density of the solid is 3.18 g cm–3

. Use this information to calculate Avogadro’s

number (Molar mass of CaF2 = 78.08 g mol

–1) 3

20. A solution prepared by dissolving 1.25 g of oil of winter green (methyl salicylate) in

99.0 g of benzene has a boiling point of 80.31 °C. Determine the molar mass of this

compound. (B.P. of pure benzene = 80.10 °C and Kb for benzene = 2.53 °C kg

mol–1) 3

21. What is the difference between multi molecular and macromolecular colloids? Give

one example of each type. How are associated colloids different from these two

types of col1oids ? 3

22. Describe how the following changes are brought about:

(i) Pig iron into steel.

(ii) Zinc oxide into metallic zinc.

(iii) Impure titanium into pure titanium. 3

OR

Describe the role of

(i) NaCN in the extraction of gold from gold are.

177

(ii) SiO2 in the extraction of copper from copper matte.

(iii) Iodine in the refining of zirconium.

Write chemical equations for the involved reactions.

23. How would you account for the following?

(i) The atomic radii of the metals of the third (5d) series of transition elements are

virtually the same as those of the corresponding members of the second (4d)

series.

(ii) The Eo value for the Mn3+/Mn2+ couple is much more positive than that for

Cr3+/Cr2+ couple or Fe3+/Fe2+ couple.

(iii) The highest oxidation state of a metal is exhibited in its oxide or fluoride. 3

24. (i) State one use each of DDT and iodoform.

(ii) Which compound in the following couples will react faster in SN2 displacement

and why?

(a) 1-Bromopentane or 2-bromopentane

(b) 1-Bromo-2-methylbutane or 2-bromo-2-methylbutane. 3

25. In the following cases rearrange the compounds as directed:

(i) In an increasing order of basic strength:

C6H

5NH

2, C

6H

5N(CH

3)

2, (C

2H

5)

6NH and CH

3NH

2

(ii) In a decreasing order of basic strength:

Aniline, p-nitroaniline and p-toluidine

(iii) In an increasing order of pKb values:

C2H

5NH

2, C

6H

5 NHCH

3, (C

2H

5)

2NH and C

6H

5NH

23

178

26. Give one example each of

(i) addition polymers,

(ii) condensation polymers,

(iii) copolymers. 3

27. What are analgesic medicines? How are they c1assifiedand when are they

commonly recommended for use? 3

28. (a) State Kohlrausch law of independent migration of ions. Write an expression

for the molar conductivity of acetic acid at infinite dilution according to

Kohlrausch law.

(b) Calculate /\om for acetic acid.

Given that /\om (HCl) = 426 S cm2 mol–1

/\om (NaCl) = 126 S cm2 mol–1

/\om (CH

3COONa) = 91 S cm2 mol–1 5

OR

(a) Write the anode and cathode reactions and the overall reaction occurring in a

lead storage battery.

(b) A copper-silver cell is set up. The copper ion concentration is 0.10 M. The

concentration of silver ion is not known. The cell potential when measured

was 0.422 V. Determine the concentration of silver ions in the cell. (Given

Eo Ag+/Ag

= + 0.80 V, Eo cu2+/cu

= + 0.34 V) 5

29. (a) Complete the following chemical equations:

(i) NaOH(aq)

+ Cl2(g)

(Hot and cone.)

(ii) XeF6(s) + H

2O(l)

179

(b) How would you account for the following?

(i) The value of electron gain enthalpy with negative sign for sulphur is

higher than that for oxygen.

(ii) NF3 is an exothermic compound but NCl

3 is endothermic compound.

(iii) ClF3 molecule has a T-shaped structure and not a trigonal planar one. 5

OR

(a) Complete the following chemical reaction equations:

(i) P4 + SO

2Cl

2

(ii) XeF4 + H

2O

(b) Explain the following observations giving appropriate reasons:

(i) The stability of + 5 oxidation state decreases down the group in group

15 of the periodic table.

(ii) Solid phosphorus pentachloride behaves as an ionic compound.

(iii) Halogens are strong oxidizing agents. 5

30. (a) Explain the mechanism of a nucleophilic attack on the carbonyl group of an

alciehyde or a ketone.

(b) An organic compound (A) (molecular formula C8H

16O

2) was hydrolysed with

dilute sulphuric acid to give a carboxylic acid (B) and an alcohol (C). Oxidation

of (C) with chromic acid also produced (B). On dehydration (C) gives but-l-

ene. Write the equations for the reactions involved. 5

OR

(a) Give chemical tests to distinguish between the following pairs of compounds:

(i) Ethanal and Propanal

(ii) Phenol and Benzoic acid

180

(b) How will you bring about the following conversions? 5

(i) Benzoic acid to benzaldehyde

(ii) Ethanal to but-2-enal

(iii) Propanone to propene

Give complete reaction in each case.

QUESTION PAPER CODE 56/1

1. What type of interactions hold the molecules together in a polar molecular solid? 1

2. What is meant by ‘limiting molar conductivity’ ? 1

3. Fluorine does not exhibit any positive oxidation state. Why? 1

4. Give the IUPAC name of the following compound: 1

H3C CH

3

=

H

H

CH3

Br

5. Write the structure of the molecule of a compound whose IUPAC name is

I-phenylpropan-2-ol 1

6. What is Tollen’s reagent? Write one usefulness of this reagent. 1

7. What is meant by ‘reducing sugars’ ? 1

8. What does the designation ‘6,6’ mean in the name nylon-6, 6 ? 1

9. Define the terms, ‘osmosis’ and ‘osmotic pressure’. What is the advantage of using

osmotic pressure as compared to other colligative properties for the determination

of molar masses of solutes in solutions? 2

181

10. Express the relation among the cell constant, the resistance of the solution in the cell

and the conductivity of the solution. How is the conductivity of a solution related to

its molar conductivity? 2

11. Given that the standard electrode potentials (Eo) of metals are:

K+ / K = – 2.93 V, Ag+ / Ag = 0.80 V, Cu 2+ / Cu = 0.34 V,

Mg2+ /Mg = - 2.37 V, Cr 3+ / Cr = – 0.74 V, Fe 2+/Fe = – 0.44 V.

Arrange these metals in an increasing order of their reducing power. 2

OR

Two half-reactions of an electrochemical cell are given below:

MnO–

4 (aq) + 8 H

+ (aq) + 5 e

– → Mn

2+ (aq) + 4 H

2O (l), E

o = + 1.51 V

Sn2+

(aq) → Sn4+

(aq) + 2 e–, E

o = + 0.15 V.

Construct the redox reaction equation from the two half-reactions and calculate the

cell potential from the standard potentials and predict if the reaction is reactant or

product favoured. 2

12. Describe the following: 2

(i) Tyndall effect

(ii) Shape-selective catalysis

13. What is meant by coagulation of a colloidal solution? Name any method by which

coagulation of lyophobic sols can be carried out. 2

14. Complete the following, chemical reaction equations: 2

(i) I2 + HNO

3

→

(cone.)

(ii) HgCl2 + PH

3

→

182

15. Draw the structural formulae of the following compounds: 2

(i) H4P

2O

5

(ii) XeF4

16. Give the chemical tests to distinguish between the following pairs of compounds: 2

(i) Ethylamine and Aniline

(ii) Aniline and Benzylamine

17. Identify A and B in each of the following processes : 2

(i) CH3CH

2Cl

(ii) C6H

5NH

2

18. Draw the molecular structures of the monomers of 2

(i) PVC

(ii) Teflon

19. The density of copper metal is 8.95 g cm–3. If the radius of copper atom be 127.8

pm, is the copper unit cell simple cubic, body-centred cubic or face-centred cubic?

(Given: atomic mass of Cu = 63.54 g mol–1 and NA = 6.02 x 1023 mol–1) 3

20. What mass of NaCl (molar mass = 58.5 g mol–1) must be dissolved in 65 g of water

to lower the freezing point by 7.50o C ? The freezing point depression constant, K

f,

for water is 1.86 K kg mol–1. Assume van’t Hoff factor for NaCl is 1.87. 3

21. Describe the role of the following: 3

(i) NaCN in the extraction of silver from a silver ore

(ii) Iodine in the refining of titanium

(iii) Cryolite in the metallurgy of aluminium

183

OR

Describe the principle involved in each of the following processes of metallurgy :

(i) Froth floatation method

(ii) Electrolytic refining of metals

(iii) Zone refining of metals

22. Explain the following cases giving appropriate reasons: 3

(i) Nickel does not form low spin octahedral complexes.

(ii) The π-complexes are known for the transition metals only.

(iii) Co2+ is easily oxidised to Co3+ in the presence of a strong ligand.

23. How would you differentiate between SN1 and S

N2 mechanisms of substitution

reactions? Give one example of each. 3

24. How would you convert the following: 3

(i) Phenol to benzoquinone

(ii) Propanone to 2-methylpropan-2-ol

(iii) Propene to propan-2-ol

25. How would you account for the following: 3

(i) NCl3 is an endothermic compound while NF

3 is an exothermic one.

(ii) XeF2 is a linear molecule without a bend.

(iii) The electron gain enthalpy with negative sign for fluorine is less than that for

chlorine, still fluorine is a stronger oxidising agent than chlorine.

26. Amino acids may be acidic, alkaline or neutral. How does this happen? What are

essential and non-essential amino acids? Name one of each type. 3

184

27. Explain the following terms with one example in each case: 3

(i) Food preservatives

(ii) Enzymes

(iii) Detergents

28. (a) Explain the following terms:

(i) Rate of a reaction

(ii) Activation energy of a reaction

(b) The decomposition of phosphine, PH3, proceeds according to the following

equation:

4 PH3 (g) P

4 (g) + 6 H

2 (g)

It is found that tile reaction follows the following rate equation:

Rate = k [PH3].

The half-life of PH3 is 37.9 s at 120

o C.

(i) How much time is required for 3/4th of PH3 to decompose?

(ii) What fraction of the original sample of PH3 remains behind after 1

minute? 5

OR

(a) Explain the following terms:

(i) Order of a reaction

(ii) Molecularity of a reaction

(b) The rate of a reaction increases four times when the temperature changes

from 300 K to 320 K. Calculate the energy of activation of the reaction,

assuming that it does not change with temperature. (R = 8.314 J K–1 mol–1)

185

29. (a) Complete the following chemical equations:

(i) Cr2O

2–

7 (aq) + H

2S (g) + H+ (aq)

(ii) Cu2+

(aq) + I– (aq)

(b) How would you account for the following:

(i) The oxidising power of oxoanions are in the order VO+

2 < Cr

2O

2–

7 <

MnO–

4.

(ii) The third ionization enthalpy of manganese (Z = 25) is exceptionallyhigh.

(iii) Cr2+ is a stronger reducing agent than Fe2+. 5

OR

(a) Complete the following chemical equations:

(i) MnO–

4 (aq) + S

2O

2–

4 (aq) + H

2O (l)

(ii) Cr2O

2–

4 (aq) + Fe2+ (aq) + H+ (aq)

(b) Explain the following observations:

(i) La3+ (Z = 57) and Lu3+ (Z = 71) do not show any colour in solutions.

(ii) Among the divalent cations in the first series of transition elements,manganese exhibits the maximum paramagnetism.

(iii) Cu + ion is not known in aqueous solutions.

30. (a) Illustrate the following name reactions giving a chemical equation in each case:

(i) Clemmensen reaction

(ii) Cannizzaro’s reaction

(b) Describe how the following conversions can be brought about:

(i) Cyclohexanol to cyclohexan-l-one

186

(ii) Ethylbenzene to benzoic acid

(iii) Bromobenzene to benzoic acid 5

OR

(a) Illustrate the following name reactions:

(i) Hell - Volhard - Zelinsky reaction

(ii) Wolff - Kishner reduction reaction

(b) How are the following conversions carried out:

(i) Ethylcyanide to ethanoic acid

(ii) Butan-l-ol to butanoic acid

(iii) Methylbenzene to benzoic acid

Write chemical equations for the involved reactions.

187

Marking Scheme ó Chemistry

General Instructions

1. The Marking Scheme provides general guidelines to reduce subjectivity in the marking.The answers given in the Marking Scheme are suggested answers. The content is thusindicative. If a student has given any other answer which is different from the one givenin the Marking Scheme, but conveys the same meaning, such answers should be givenfull weightage.

2. The Marking Scheme carries only suggested value point for the answers. These areonly guidelines and do not constitute the complete answers. The students can havetheir own expression and if the expression is correct the marks, will be awardedaccordingly.

3. Some of the questions may relate to higher order thinking ability. These questions havebeen indicated by the mark* and the students understanding/analytical ability may bejudged. These questions are to be evaluated carefully.

4. The Head-Examiners have to go through the first five answer-scripts evaluated byeach evaluator to ensure that the evaluation has been carried out as per the instructiongiven in the marking scheme. The remaining answer scripts meant for evaluation shallbe given only after ensuring that there is no significant variation in the marking of individualevaluators.

5. Evaluation is to be done as per instructions provided in the Marking Scheme. It shouldnot be done according to one's own interpretation or any other consideration - MarkingScheme should be strictly adhered to and religiously followed.

6. If a question has parts, please award marks in the right hand side for each part. Marksawarded for different parts of the question should then be totalled up and written in theleft hand margin and circled.

7. If a question does not have any parts, marks be awarded in the left-hand margin.

8. If a candidate has attempted an extra question, marks obtained in the question attemptedfirst should be retained and the other answer should be scored out.

9. No Marks to be deducted for the cumulative effect of an error. It should be penalizedonly once.

10. A full scale of marks 0-70 has to be used. Please do not hesitate to award full marksif the answer deserves it.

188

QUESTION PAPER CODE 56/1/1

EXPECTED ANSWERS/VALUE POINTS

1 Mode of conduction, through electrons in solid metal and through ions in molten

state or in solution in ionic solid / Metals are malleable and ductile whereas ionic

solids are hard and brittle. 1

2 The sum of powers of the concentration of the reactants in the rate law expression

is called the order of that chemical reaction. 1

3 Emulsions are liquid-liquid colloidal systems. 1

4 Because NO2 contains odd number of valence electrons and on dimerisation it is

converted to stable N2O

4 molecule with even number of electrons. 1

5 [Co(NH3)

5(NO

2)]Cl

2 and[Co(NH

3)

5(ONO)]Cl

2 (or any other correct example) 1

6 CH3 CHCl CH

2CH

31

7 Ph – CO – CH2-CH

31

8 But-3-en-1-amine 1

9 When the vapour pressure of a non-ideal solution is either higher or lower than that

predicted by Raoult’s law, the solution exhibits deviations. ½

These deviations are caused because of unequal intermolecular attractive forces

between solute-solvent molecules and solute-solute or solvent-solvent molecules. ½

Positive deviation eg: mixture of ethanol and acetone, carbon-disulphide and ace-

tone (any one) ½

Negative deviation eg: Chloroform and acetone, nitric acid and water (any one) ½

10 Rate = k[A][B]2

(i) When the concentration of B is increased to 3 times, then rate would be

Rate = k[A][3B]2 ½

189

= 9k[A][B]2

= 9 times the initial Rate1 i.e. rate is increased 9 times ½

(ii) When the concentration of A as well as B are doubled, then rate would be

Rate = k[2A][2B]2 ½

= 8k[A][B]2

= 8 times the initial Rate i.e. rate is increased 8 times ½

11 [R]t = - kt + [R]

0½

0.075M = - (0.0030 mol L-1 s-1)t + 0.10M ½

-0.025M = -(0.0030 mol L-1 s-1)t

t = 8.3s 1

12

½, ½

White Phosphorus Rod Phosphorus

White phosphorus is more reactive due to its discrete tetrahedral structure and

angular strain 1

13 (i) Due to decrease in size and increasing mass.

(ii) Because of variable oxidation states exhibited by them. 1+1

14 (i) Tetraammineaquachloridocobalt(III) chloride

(ii) Dichloridobis(ethane-1,2-diamine)chromium(III) chloride 1+1

15 (i) Kolbe’s Reaction

P

P

P

P

P

P

P

– P

P

P

P

– P

P

P –

P

– P

190

(ii) Williamson Synthesis

RONa + R’Br → R – O – R’ + NaBr 1

Where R and R’ are alkyl groups.

16 (i)

(ii)

O | | OMgBr OH

CH3–C– CH

3| H

2O |

CH3MgBr CH

3 – C – CH

3 CH

3 – C – CH

31

| |

CH3

CH3

(or any other suitable method)

17 i) Invert sugar: Hydrolysis of sucrose brings about a change in a sign of rotation

from dextro (+) to laevo (-) and the product is named as invert sugar 1

ii) Polypeptides are the polymers of amino acids. 1

OR

Products of hydrolysis of sucrose are : Glucose and Fructose 1

Becuase Carbonyl group of sucrose is not free 1

OH ONa OH

COOHNaOH (i) CO

2

(ii) H+

2-Hydroxybenzolc acid

(Salicylio acid)

1

CH2– CI CH

2– OH

ag.NaOH

191

18 Amino acids which must be supplied in our diet are called Essential Amino Acids

eg. Leucine, Isoleucine, Valine (any one) ½ + ½

Amino acids which can be made by our bodies and not required in our diet are

called non-essential Amino Acids eg. Glycine, Alanine (any one) ½ + ½

19 d = z x Ma3 x N

A

For fcc lattice z = 4 1

3.18 g cm-3 =

4 x 78.08 g mol -1

( 5.46 x 10 -8 cm )3 x NA

1

NA =

4 x 78.08 g mol -1

( 5.46 x 10 -8 cm )3 x 3.18 g cm-3

NA = 6.033 x 1023 mol -1 1

20 ∆ Tb = (80.31 – 80.10)0C = 0.210C or 0.21 K

∆ Tb = K

b m 1

0.21 °C = 2.53 °C kg mol-1 x 1.25g x 1000

M 99kg 1

M ò 152 g mol -1 1

Where M is molar mass of the solute

21 Multimolecular colloids Macromolecular colloids

They are aggregates of molecules They themselves are large molecules

less than 1nm thick. of colloidal dimensions ½+½

Example :Sulphur Sol Example :Starch ½+½

Associated colloids – are those which at low concentration behave as normal elec-

tolytes & at high concentration act as colloids. 1

192

22 i) Pig iron is converted into steel by adding carbon and some other elements.

ii) Metallic Zinc is obtained from Zinc oxide by reduction with coke.

ÄOr ZnO + C Zn + CO

iii) Impure titanium is heated with Iodine to form volatile complex TiI4 which

on further heating to higher temperature decomposes to give pure titanium. 1x3 = 3

(or Chemical Equations to represent the above reactions)

OR

(i) Role of NaCN in the extraction of gold is to do the leaching of gold ore inthe prescence of air from which the gold is obtained later by replacement. 1

or

4Au(s) + 8CN-(aq) + 2H2O + O

2(g) 4[Au(CN)

2]- + 4OH-

(ii) SiO2 is added in copper matte to convert the remaining FeS, FeO to slag. 1

or

FeO + SiO2 FeSiO

3(slag)

(iii) Iodine is heated with Zirconium to form a volatile compound which on furtherheating decomposes to give pure zirconium as shown: 1

Zr(impure) + 2I2 ZrI

4

ZrI4 Zr(pure) + 2I

2

23 (i) Due to Lanthanoid Contraction / or its meaning

(ii) Due to stable half –filled 3d5 configuration of Mn2+ / high 3rd ionisation enthalpy

of Mn.

(iii) Becuase Oxygen or Fluorine is highly electronegative and small size element. 1x3 = 3

24 (i) DDT is used as an insecticide and Iodoform is used as a mild antiseptic. ½ + ½

(ii) (a) 1-Bromo pentane, as it is a primary alkyl halide. ½ + ½

(b) 1-Bromo-2-methyl butane, as it is a primary alkyl halide. ½ + ½

193

25 (i) C6H

5NH

2 < C

6H

5N(CH

3)

2 < CH

3NH

2 < (C

2H

5)

2NH

(ii) p-toluidine > Aniline > p-nitroaniline

(iii) (C2H

5)

2NH < C

2H

5NH

2 < C

6H

5NHCH

3 < C

6H

5NH

21x3 = 3

26 (i) Polythene, PVC, (or any other one example)

(ii) Nylon-6,6, Nylon-6, Terylene (or any other one example)

(iii) Buna-S, Buna-N (or any other one example) 1x3 = 3

27 The chemical substances which are used to relieve pain. 1

These are of two types: (i) Non narcotic Drugs

(ii) Narcotic Drugs 1

Non Narcotic Drugs are effective in relieving skeletal pain / preventing heart attack /

viral inflammation, etc. ½

Narcotic Drugs are recommended for the relief in postoperative pains / Cardiac

pain / terminal cancer. ½

28 (i) The law states that limiting molar conductivity of an electrolyte can be rep-

resented as the sum of the individual contributions of the Anion and Cation

of the electrolyte. 1

Ë °m (HAc)

= ë°H+

+ ë°Ac

- 1

(ii)∧ o

CH3COOH =∧ o

CH3COONa +∧ o

HCI – ∧ o

NaCI 1

= ( 91 + 426 – 126 )S cm2 mol-1 1

= 391 S cm2 mol

-1 1

OR

194

(i) Anode Reaction : - Pb + SO42– ? PbSO

4(s) + 2e– ½

Cathode Reaction : - PbO2 + 4H+ + SO

42– + 2e– → PbSO

4 + 2H

2O ½

Net reaction:- Pb + PbO2 + 2SO

42– + 4H+ → 2PbSO

4 + 2H

2O 1

(ii) The cell reaction : Cu(s) + 2 Ag+ (aq) → Cu2+ (aq) + 2 Ag(s)

Eo

cell = 0.80 V – 0.34V = 0.46V ½

Nernst equation

Ecell

= Eo

cell - 0.059 log [ Cu2+] 1

2 [ Ag+]2

Ecell = 0.46V - 0.059 log [ Cu2+] ½

2 [ Ag+]2

0.422V = 0.46 V - 0.059 log 0.10

2 [Ag+]2 1

log 0.10 = 1.2881

[Ag+]2

(Full marks to be awarded upto this stage)

[Ag+]2=0.0051

[Ag+] = 7.1x10-2 M

29 (a) (i) 6NaOH + 3Cl2 5NaCl + NaClO

3 + 3H

2O 1

(ii) XeF6 + H

2O XeOF

4 + 2HF

or

XeF6 + 2H

2O XeO

2F

2 + 4HF

or

XeF6 + 3H

2O XeO

3 + 6HF 1

195

(b) (i) Becuase of larger size of sulphur atom than oxygen atom.

(ii) Becuase bond energy of F2 is lower than Cl

2 and N-F bond is smaller

& stronger than N-Cl bond.

(iii) Becuase it has sp3d hybridization. 1x3 = 3

OR

(a) (i) P4 + 10SO

2Cl

2 4PCl

5 + 10SO

2

(ii) 6XeF4 + 12H

2O 2XeO

3 + 4Xe + 24HF + 3O

21+1

(Note: Assign marks for correct products.)

(b) (i) Becuase down the group, +3 oxidation state becomes more & more

stable due to higher energy involved to unpair the s electrons / due to

inert pair effect.

(ii) Due to the formation of [PCl4]+ [PCl

6]-

(iii) Becuase they readily accept an electron. 1x3 = 3

30 (a)

2

196

(b)

CH3CH

2CH

2COOCH

2CH

2CH

2CH

3 CH

3CH

2CH

2COOH + CH

3CH

2CH

2CH

2OH

A B C

CH3CH

2CH

2CH

2 OH

CH

3CH

2CH

2COOH

CH3CH

2CH

2 CH

2OH CH

3CH

2CH=CH

21x3 = 3

OR

(a) Ethanal and Propanal

Iodoform test. Warm each compound with iodine and sodium hydroxide on

a water bath.

Propanal (CH3CH

2CHO) No yellow ppt formed

Ethanal (CH3CHO) Yellow crystals of Iodoform are formed. 1

(Other relevant test can be accepted)

(ii) Phenol and Benzoic acid.

FeCl3 test. Add a few drops of neutral FeCl

3 solution. 1

Phenol (C6H

5OH), violet coloured ppt. is produced.

Benzoic acid (C6H

5COOH), no ppt. is produced.

(Other relevent test can be accepted)

(b) (i)

OH|

(ii) 2CH3– CHO CH

3 –CH – CH

2– CHO CH

3– CH = CH – CHO

(iii) CH3– C – CH

3CH

3 – CH – CH

3CH

3 – CH = CH

21x3 = 3

|| |O OH

(Or by any other suitable method.)

COOH COCI CHO

PCls H2,pd-BaSo

4

197

QUESTION PAPER CODE 56/1

EXPECTED ANSWERS/VALUE POINTS

1 Dipole – Dipole interaction 1

2 It is molar conductivity at infinite dilution or approaching zero concentration 1

3 Because Fluorine is the most electronegative element. 1

4 4-bromo-3-methyl pent-2-ene 1

5 C6H

5-CH

2-CH(OH)-CH

31

6 Ammoniacal solution of silver nitrate is called Tollen’s reagent. It is used as an oxidi-

zing reagent / test for –CHO group. ½ + ½

7 Carbohydrates which reduce Tollen’s reagent or Fehling solution are called reducing

sugars which have free aldehydic group. 1

8 6,6 means the number of carbon atoms in the monomers of Nylon-6,6 1

9 The flow of solvent from solution of low concentration to higher concentration through

semipermeable membrane is called osmosis. ½

The hydrostatic pressure that has to be applied on the solution to prevent the entry

of the solvent into the solution through the semipermeable membrane is called the

Osmotic Pressure. ½

Advantage: Unlike other colligative properties, osmotic pressure is used to deter-

mine the Molar mass of macromolecules/polymers like protein / or any other advan-

tage 1

10 k = 1/R (l/A) 1

Where k is conductivity, R is resistance and l/A is cell constant

Ëm = k/C 1

Where Ëm is molar conductivity and

C is concentration of the solution

198

11 Ag+ / Ag < Cu2+ / Cu < Fe2+ / Fe < Cr3+ / Cr < Mg2+ / Mg < K+ / K 2

OR

Redox Reaction

2MnO4- + 5Sn2+ + 16H+ 2Mn2+ + 5Sn4+ + 8H

2O 1

E°cell

= E°C-E°

A

= (+1.51 – 0.15)V = +1.36V ½

As E°cell

is positive, the reaction is product favoured ½

12 Tyndall Effect:- The scattering of light by the colloidal particles present in a colloi-

dal sol is called Tyndall effect 1 + 1

Shape Selective Catalysis:- The catalytic reaction that depends upon the pore

structure of the catalyst and the size of the reactant and product molecules is called

shape-selective catalysis.

13 Coagulation is a process of aggregating together the colloidal particles so as to

change them into large particles which ultimately settle as a precipitate. 1

By electrophoresis, coagulation of lyophobic Sols can be carried out / or any other

method. 1

14 (i) I2 + 10HNO

3 2HIO

3 + 10NO

2 + 4H

2O 1+1

(ii) 3HgCl2 + PH

3 Hg

3P

2 + 6HCl

Note: Assign marks for correct products.

15 (i)

HO H O

P P OH

O O H 1+1

199

16 Ethylamine and aniline

Aniline forms an azo-dye with benzenediazoniumchloride through couplingreaction whereas ethylamine does not form an azo-dye. 1

Aniline and benzylamine

Aniline forms an azo-dye with benzenediazoniumchloride through couplingreaction whereas benzylamine does not form an azo-dye. 1

(or any other suitable test)

17 (i) A = CH3 – CH

2 – CN B = CH

3 CH

2 CH

2 NH

3½ + ½

(ii) A = C6 H

5 N

2

+ Cl

–B = N = N NH

2½ + ½

18 (i) CH2=CH-Cl 1 + 1

(ii) CF2=CF

2

19 d = z x M__ 1

a3 x NA

Assuming fcc lattice for copper

a = 2v2 r

a3 = (2v2 r)3 = 8 x 2v2 (1.27 x 10-8cm)3

= 4.723 x 10-23cm3 1

d = 4 x 63.54 g mol-1

4.723 x 10-23 cm3 x 6.02 x 1023 mol-1

= 8.94 g cm-3 1

Note: If any other lattice is assumed, comparing the density or z-value with

the given one, may be accepted as the right procedure.

200

20 ∆ Tf = 7.50C

∆ Tf = iK

f m 1

7.50C = 1.87 x 1.860C kg mol-1 xw

x1000 1

58.5g mol-1

65 kg

w = 8.2g 1

21 (i) Role of NaCN in the extraction of silver is to do the leaching of silver ore in

the prescence of air from which the silver is obtained later by replacement. 1

or

4Ag(s) + 8CN–(aq) + 2H2O + O

2(g) 4[Ag(CN)

2]– + 4OH–

(ii) Iodine is heated with titanium to form a volatile compound which on further

heating decomposes to give pure titanium. 1

or

Ti(impure) + 2I2 TiI

4

TiI4 Ti(pure) + 2I

2

(iii) Cryolite lowers the melting point of mixture of alumina in the extraction of

aluminium / increase the conductivity of mixture. 1

OR

(i) Froth Floatation method:- The mineral particles become wet by oils while

the gangue particles by water.

(ii) Electrolytic refining: Crude metal is made as anode and pure metal as cath-

ode. When current is passed through electrolyte of same metal ions then pure

metal gets deposited at cathode and impurities settle at bottom of anode.

(iii) Zone Refining:- The impurities are more soluble in the melt than in the solid

state of the metal. 1x3 = 3

201

22 (i) Because two inner d-orbitals are not available in Ni. 1x3 = 3

(ii) Because only d-electrons can be involved in ð-complex.

(iii) Because crystal field splitting energy is more than compensated for the third

ionisation enthalpy.

23 In SN1 it occurs in two steps and the reaction is of first order whereas in S

N2 it

occurs in one step and the reaction is of second order.

or 1

In SN1 reaction, retention of configuration takes place whereas in S

N2 inversion of

configuration occurs.

SN2 example:

H H H–OH + H C1 HO C1 HO H + Cl

–1

H H H H

SN1 example:

CH3

(CH3)

3 CBr + + Br

–

CH3

H3C CH

3

+ + –OH (CH

3)

3COH

H3C CH

3

24 (i) OH O

O

202

CH3

|

(ii) CH3 – C – CH

3 – CH

3 – C – CH

3

| | |

O OH

(iii) CH2 = CH – CH

3 CH

3 – CH – CH

31x3 = 3

|

OH

25 (i) Because (a) bond dissociation enthalpy of F2 is lower than that of Cl

2 and

(b) small size F atom forms stronger bond with N. 1x3 = 3

(ii) Because it has sp3d hybridization with 3 lone pairs.

(iii) Because of (a) lower bond dissociation enthalpy of F2 and

(b) high hydration enthalpy of F

26 Acidic amino acids contain more number of carboxyl groups than amino groups.

Basic amino acids contain more number of amino groups than carboxyl groups.

Neutral amino acids contain equal number of amino acids and carboxyl groups. 1

(or any other suggestive answer)

Those amino acids which must be supplied in our diet are called essential amino

acids and those which can be made by our bodies and not required in our diet are

called non-essential amino acids. 1

Essential amino acids: Valine, leucine, isoleucine, argenine (any one)

Non Essential amino acids: Glycine, alanine (any one) 1

27 (i) Food preservatives: are the compounds which prevent spoilage of food due

to microbial growth. eg: sodium benzoate, vinegar (any one example) ½+½

(ii) Enzymes are the biological catalysts which increase the rate of metabolism.

eg: Invertase, Zymase, (or any other one example) ½+½

203

(iii) Detergents are sodium salts of long chain alkyl sulphonates or benzene sulp-

honates. eg: Sodium Lauryl sulphate. ½+½

28 (a) (i) Rate of a reaction- Rate of Change of concentration of reactant or pro-

duct with time is called rate of reaction

(ii) Activation Energy – Minimum energy which the reacting molecules

should acquire so that they react to give product is called activation

energy. 1+1

or

The energy required by the reactant molecules for the formation of intermediate

activated complex

(b) (i) t 1/2

= 0.693 ½

k

k = 0.693 s-1

37.9

k = 0.0183s–1

t = 2.303 log [ A0 ] ½

0.183s-1 [A]

t = 2.303 log 1 . 1

0.183s-1 1/4

t = 75.84s

(ii) k = 2.303 log [ A0 ]

60s [A]

log [ A0 ] = k x 60

[A] 2.303

= 0.0183 x 60

2.303

204

log [ A0 ] = 0.4762 1

[A]

(Full credit may be given upto this stage)

[ A0 ] = 2.999

[A]

Therefore, [ A ] = 0.33

[A0]

OR

(a) (i) The sum of powers of the concentration of the reactants in the rate law

expression is called the order of that chemical reaction.

(ii) Molecularity – Number of molecules taking part in rate determining

step of a reaction is called molecularity 1+1

(b) log k2 = Ea × T

2- T

1

k1 2.303 R T

1 T

21

log 4 = Ea × 320- 300 K-1 1

2.303 x 8.314 JK-1 mol-1 300 x 320

0.6020 = Ea ×

20 K-1

2.303 x 8.314 JK-1 mol-1 96 x 103

Ea = 55336.7 J mol-1

= 55.33 kJ mol-1 1

29 (a) (i) Cr2O

72- + 3H

2S + 8H+ 2Cr3+ + 7H

2O + 3S

(ii) 2Cu2+ + 4I– Cu2I

2 + I

21+1

(b) (i) It is due to increasing stability of lower species to which they are red-

uced.

205

(ii) Because removing 3rd e- from extra stable 3d5 configuration is difficult

in case of Mn

(iii) Because d3 of Cr2+ is more stable than d5 of Fe3+ 1x3 = 3

OR

(i) 8MnO4- + 3S

2O

32- + H

2O 8MnO

2 + 6SO

42- + 2OH-

(ii) Cr2O

72- + 14H+ + 6Fe2+ 2Cr3+ + 6Fe3+ + 7H

2O 1+1

(b) (i) In La3+, there is no f electrons while in Lu3+, there is presence of f14 /

absence of unpaired electron / due to d-d transition.

(ii) Mn2+ has 3d5 configuration having 5 unpaired electrons

(i) Cu+ undergoes disproportionation in aqueous solution. 1x3 = 3

or

2Cu+ Cu2+ + Cu

30 (a) (i) Clemmensen reduction

Zn - HgC = O CH

2 + H

2O

HC1

(a) (ii) Cannizzaro reaction:

H HC = O + C = O + KOH (conc.)

H H

formaldehyde

H O

|

H – C – OH + H – C|

H OK

Methanol sodium formate

206

(b) (i) OH O

(i) C2H

5COOH

(iii) Br MgBr COOMgBr COOH

1x3 = 3

(or by any other suitable method)

OR

(a) (i) Hell-Volhard-Zelinsky reaction

R-CH2–COOH R – CH – COOH

| 1

X

X = Cl, Br

(ii) Wolf-kishner reduction

C = O C = NNH2

CH2 + N

21

(wolff-Kishner rduction)

(b) (i) C2H

5 – CN CH

3 – CH

2 – CONH

2 CH

3 – CH

2 – NH

2

CH3 – CH

2 – OH

CH

3COOH

(ii) CH3 – CH

2 – CH

2 – CH

2 – OH

CH

3 – CH

2 – CH

2 – COOH 1x3 = 3

(i) CH3

COOH